Translating the Mechanisms of Hypoxia to Long-Term Oxygen Prescription in COPD: A Proposal.

Abstract

Current indications for long-term oxygen therapy (LTOT) primarily are based on thresholds of arterial oxygen saturation (Sao₂) or Pao₂ that ignore fundamental mechanisms of adaptation and intolerance to hypoxia. In individuals exposed to chronic hypoxic conditions, the accumulation of hypoxia-inducible factors in the cell nucleus upregulates target genes that favor tolerance to hypoxia. Adaptations include hyperventilation, systemic vascular bed development, increased erythropoiesis, and cellular metabolic adjustments. Excessive responses to hypoxia also may develop, leading to pulmonary vasculature remodeling and other end-organ dysfunctions. Biomarkers of hypoxia may complement the measurement of Sao₂ or Pao₂ in personalizing oxygen prescription before end-organ dysfunction becomes clinically apparent. From a scoping review of the literature, we identified several biomarkers that reflect the basic mechanisms of hypoxia at the cellular level in COPD. Although hypoxia-inducible factors are central to these mechanisms, the determination of their plasmatic concentration for clinical purposes currently is not well validated. Candidate biomarkers to guide LTOT prescription include circulating levels of hemoglobin, erythropoietin, brain natriuretic protein, and endothelin-1, as well as macroalbuminuria. Because response to oxygen may be determined genetically, genotyping potentially may serve as an additional method to personalize LTOT prescription. Prescribing LTOT solely based on Sao₂ or Pao₂ thresholds may be inappropriate. According to precision medicine principles, we propose that it should be a priority to identify early indicators of adverse reactions to chronic hypoxia and to validate their usefulness in deciding who should receive LTOT.